Air purifier

ABSTRACT

To enhance the dust collecting efficiency and to make it possible to collect dust of relatively large particle sizes in a compact construction, an air purifier comprises dust collecting wall means including a dust collecting electrode and extending helically to provide a continuous helical passageway for air to be circulated in the air purifier and at least one charging electrode also helically extending in the passageway for establishing an electric field in the passageway through application of a high-tension current to be collecting electrode or to the charging electrode. Dust particles are collected by the dust collecting wall means by reason of the centrifugal forces imparted to the particles and the electrostatic attraction exercised on the particles as the air is passed through the passageway. Also proposed is an improved automotive air conditioning and cleaning system in which either atmospheric air or a mixture of the atmospheric air and air recirculated from a passenger compartment is cleaned before it is directed into the passenger compartment.

- United States Patent 1191 Ha yashi [4 1 Dec. 10,1974

[ AIR PURIFIER [75] Inventor: Kazuo Hayashi, Yokohama, Japan [73] Assignee: Nissan Motor Company, Limited,

Yokohama, Japan [22] Filed: June 1, 1973 [21] Appl. No.: 365,851

[] Foreign Application Priority Data Nov. 29, 1972 Japan 47-137325 Nov. 29, 1972 Japan... 47-137328 Nov. 29, 1972 Japan. 47-137326 [52] US. Cl 55/124, 55/127, 55/134,

317/4, 262 R, 262 AB [56] References Cited UNITED STATES PATENTS 1,015,786 l/19l2 Coyle 261/D1G. 34 1,773,840 8/1930 Nattcher et al.... /127 1,819,643 8/1931 Fleisher 261/1310. 34

1,843,839 2/1932 Ruder 55/127 2,058,042 10/1936 Shipman. 62/171 2,144,693 1/1939 Seid 26l/D1G. 34 2,974,747 3/1961 Coolidge, Jr. et al. 55/124 X MessenJaschin' 55/114 3,421,291 l/l969 3,440,800 4/1969 Messen-Jaschin 55/122 3,563,004 2/1971 Schouw 55/127 X 3,592,541 7/1971 Gourdine 355/17 3,656,440 4/1972 Grey /119 X 3,722,183 3/1973 Gaylord 55/128' FOREIGN PATENTS OR APPLICATIONS 714,821 9/1931 France 55/138 730,960 5/1932 France 55/127 1,029,116 3/1953 France 55/124 931,625 7/1963 Great Britain 55/139 Primary ExaminerDennis E. Talbert, Jr.

[57] ABSTRACT To enhance the dust collecting efficiency and to make it possible to collect dust of relatively large particle sizes in a compact construction, an air purifier comprises. dust collecting wall means including a dust collecting electrode and extending helically to provide a continuous helical passageway for air to be circulated in the air purifier and at least one charging electrode also helically extending in the passageway for establishing an electric field in the passageway through application of a high-tension current to be collecting electrode or to the charging electrode. Dust particles are collected by the dust collecting wall means by reason of the centrifugal forces imparted to the particles and the electrostatic attraction exercised on the particles as the air is passed through the passageway. Also proposed is an improved automotive air conditioning and cleaning system in which either atmospheric air or a mixture of the atmospheric air and air recirculated from a passenger compartment is cleaned before it is directed into the passenger compartment.

7 Claims, 9 Drawing Figures PATENTEL DEC] 3.853.512

' I sum 2 OF 5 PATENTEL DEC! 0 I974 SHEEI 5 OF 5 AIR PURIFIER The present invention relates to an air purifier and, more particularly, to an air purifier of the dust collector type adapted to remove dust from atmospheric air.

A primary object of the present invention is to provide an improved air purifier having an enhanced dust collection efficiency and capableof collecting dust of relatively large particle sizes.

Another important object of the invention is to provide an improved air purifier which meets serious space requirements such as in buses and automobiles.

To accomplish these objects,(an air purifier herein proposed is characterized in that it operates on the principles of operation of a centrifugal dust separator and an electrostatic dust precipitator which per se are well known in the art.

In accordance with the present invention, the air purifier consists essentially of a generally cylindrical casing having an air inlet opening which is directed substantially tangentially of the casing and an'air outlet opening which is located substantially centrally of the casing, dust collecting wall means positioned within the casing and providing a continuous passageway helically extending between the air inlet and outlet openings, the wall means including at least one dust collecting electrode for connection to one electric terminal, and at least one charging electrode helically extending in and along the passageway and electrically isolated from the collecting electrode, the charging electrode'being for connection to another electric terminal having a polarity opposite to the polarity of the terminal for the collecting electrode for thereby establishing an electric field between the charging andcollecting electrodes so that particles of dust entrained in an air stream directed into the passageway through the air inlet opening beand the ability of collecting relatively large dust particles, anair purifier of the general configuration above described willprovide advantageous especially where used in a motor vehicle in which only a limited amount of space is available for incorporating the air purifier.

Other features and advantages of an air purifier according to. the present invention will be more apparent from the following description taken in conjunction with the accompanying drawings in which like reference numerals and characters designate corresponding parts and members throughout the figures and in which:

FIG. 1 is a cross sectional view of a first preferred embodiment of an air purifier according to the-present invention;

FIG. 2 is a side sectional view of the air purifier illustrated in FIG. 1;

FIG. 3 is a longitudinal sectional view showing on an enlarged scale of preferred example of an arrangement to support a charging electrode in the air purifier illustrated in FIGS. 1 and 2;

FIG. 4 is a cross sectional view showing a second preferred embodiment of an air purifier according to the present invention;

FIG. 5 is a side sectional view of the air purifier illustrated in FIG. 4;

FIG. 6 is a fragmentary perspective view showing on an enlarged scale a preferred example of a safety ar rangement to be incorporated into the air purifier according to the present invention,

FIG. 7 is a schematic view showing an electric circuit including a switch means to be incorporated inthe safety arrangement illustrated in FIG. 6;

FIG. 8 is a cross sectional view showing a third preferred embodiment of an air purifier according to the present invention; and

FIG. 9 is a side sectional view of the air purifier illustrated in FIG. 8.

Reference will now be made to the drawings, first to FIGS. 1 and 2 which illustrate a first preferred embodiment of an air purifier according to the present invention.

As seen in FIGS. 1 and 2, the air purifier embodying the present invention includes a generally cylindrical casing which is designated in its entirety by reference numeral 20. The casing 20 is formed of an electrically non-conductive material and comprises a generally cylindrical wall 22 and upper and lower end walls 24 and 26, respectively. The casing 20 has formed in its cylindrical wall 22 and opening 28 through which an air inlet duct 30 projects into the casing 20 substantially tangential to the inner surface of the cylindrical wall 22 as seen in FIG. 1. Approximately centrally of the upper wall 24 of the casing 20 is formed an opening 32 which is in communication with an air outlet duct 34.

Within the casing 20 is positioned a dust collecting electrode 36 which spirals inwardly from a leading end 30a of the air inlet duct 30 toward the center of the casing 20, terminating substantially in alignment with the air outlet opening 32 in the upper end wall 24 of the casing 20. The outermost segment of the dust collecting electrode 36 is attached to the inside of the cylindrical wall 22 along a portion thereof, and comprises a radially outer layer 38, a radially intermediate layer 40 of a dust collecting filter attached to the inner surface of the outer layer 38, and an electrically conductive porous or meshed radially inner layer 42 attached to the inner surface of the intermediate layer 40. The collecting electrode 36 extends for substantially one complete spiral revolution within the casing 20 having the configuration described above, and merges at the end 30a with a portion thereof which spirally extends further inward, but has an altered configuration which will now be described. Theinner portion of the dust collecting electrode 36 comprises an electrically conductive intermediate layer 38' electrically connected to the outer layer 38, a pair of layers 40' and 40" of a dust collecting material attached to the radially outer and inner surfaces, respectively, of the intermediate layer 38'. and a pair of electrically conductive porous or meshed outer layers 42 and 42" attached to the radially outer and inner surfaces of the layers 40- and 40", respectively, of the dust collecting material. the layers 40" and 42" thus extending continuously from the layers 40 and 42, respectively. The layers 40, 40 and 40" of dust collecting material are preferably formed of unwoconductive layers 42, 42' and 42" through an electrically conductive plate 44.

- The dust collecting electrode 36 thus configured defines a continuous passageway 46 spirally extending from the leading end 30a of the air inlet duct 30 to a substantially central portion 48 of the interior of the casing 20, thus providing unrestricted communication between the air inlet duct 30 and the air outlet duct 34, as seen in FIG. 1.

A suitable numberof charging electrodes 50, shown in FIG. 2 as being two in number by way of example, spirally extend substantially centrally within the passageway 46 and terminate at their inner ends in the vicinity of the central portion 48 of the interior of the casing 20. The charging electrodes 50 are spaced apart from each other along the axis of the casing and are supported from the upper end wall 24 of the casing 20 by a number of electrically conductive rods or wires 52 as seen in FIG. 2. The charging electrodes 50 may have their outer ends located immediately downstream of to the leading end a of the air inlet duct 30 or, where desired, the electrodes 50 may have their outer ends appropriately spaced from the leading end 30a of the air inlet duct 30, as in the embodiment illustrated in FIG. 1. Where the charging electrodes 50 are disposed in a manner illustrated in FIG. 1, an additional charging electrode 54 in a rod form may be located at the entrance of the passageway 46 for preliminarily charging the or ionizing the dust particles before the air to be cleaned reaches the electrodes 50. In this instance, the electrode 46 serves to augment the electric field between the electrodes 50 and the dust collecting electrodes 36 on both sides thereof.

Wiring arrangements are made so that the charging electrodes 50 and 54 are energized to a polarity opposite to the polarity of the dust collecting electrode'36. Thus, one of the conductive rods or wires 52 is electrically connected to a source (not shown) of high dc voltage through alead 56 and a joint 58 which is attached to the upper end wall 24 of the casing 20, while the dust collecting electrode 36 or more particularly the electrically conductive layers 38 and 38' are connected to ground through a line 60. It is, in this instance, preferable that the charging electrode 54 be supplied with a dc voltage which is equal to or higher than the voltage applied to the spiral charging electrode 50. The wiring arrangements above described charge the dust particles to a positive polarity but, where desired, the arrangement may be reversed so that the dust collecting electrode 36 is connected to the positive electrical source terminal and the charging electrodes 50 and 54 are connected to ground for charging the dust particles to a negative polarity. The conductive rods or wires 52 excepting the one connected to the lead 56 are supported at the upper end wall 24 of the casing by means of retainers 62, each comprising a rivet 62a and a spacer 62b by which the rod or wire 52 is adjustably attached to the end wall 24.

Where desired, the lower end wall 26 of the casing 20 may be formed with an opening 64 located in alignment with the air outlet opening 32 in the upper end wall 24 for allowing relatively heavy dust particles to drop out of the casing 20 before the cleaned air is discharged from the air outlet opening 32. In this instance, a dust reservoir 66 may be releasably supported at the lower surface of the lower end wall 26 of the casing 20 so that dust particles dropping from the interior of the casing 20 are deposited in the reservoir 66. The lower end wall 26 and the adjacent dust collecting electrode 36 are releasably connected to the cylindrical wall 22 of the casing 20 so that the end wall 26 and the dust collecting electrode 36 can be removed from the casing 20 for dislodging the dust deposited on the dust collecting layers 40, 40' and 40" of the dust collecting electrode 36.

FIG. 3 illustrates a preferred example of the joint 58 through which a conductive rod or wire 52 is connected to the lead 56. As seen in FIG. 3, the joint 58 comprises a flanged, internally threaded retaining member 68 which is received in the upper end wall 24 of the casing 20 with its flange fast on the upper surface of the end wall 24 and its inner end projecting into the interior of the casing 20. The retaining member 68 serves as a washer and is secured to the .end wall 24 by means of a snap ring 70 which is fast on the inner surface of the end wall 24. The conductive rod or wire 52 is threaded at its upper end portion 520 and screwedly received in the retaining member 68 with its tip projecting from the upper end of the retaining member 68. An internally and externally threaded member 71 securely receives in its internally threaded bore the upper end portion 52a of the rod or wire 52 and rests on the upper face of the retaining member 68. The rod or wire 52 is connected at its end to the lead 56 through a snap connection 72 which may be configured in the form of a ball and socket joint. The threaded member 71 and the snap connection 72 are enclosed within acup-like cap member 74 having an internally threaded portion by which the cap member 74 screws onto the threaded member 71. The cap member 74 has formed at its top an aperture 74a through which the lead 56 passes through the cap member 74. Where desired, the cap member 74 may be formed with a projection 74b on its inner surface for engagement with the upper surface of the threaded member 71. The retaining member 68, threaded member 71 and cap member 74 are all formed of electrically insulating materials. A joint arrangement of the nature above described is merely for the purpose of illustration and, as such, is subject to various modifications and changes where desired.

Where the air purifier thus far described is placed in practical use, it is important that the same be arranged in combination with a blower or suction fan for achieving forced circulation of air through the air purifier. When, thus, the fan associated with the air purifier is driven and the charging electrodes 50 and 54 are energized from the source of high-tension dc., voltage, air entering the passageway 46 from the air inlet duct 30 is passed through the electric field established between the electrode 54 and the dust collecting electrode 36 on both sides of the former. Particles of dust contained in the stream of air become ionized to a positive polarity and then move into the electric field built up on both sides of the spiral electrode 50. The dust particles are then attracted to the grounded electrically conductive layers of the dust collecting electrode 36 and are deposited on the intermediate dust collecting layers 40, 40' and 40" of the electrode 36 as the air flows through the spiral passageway 46 toward the substantially central portion 48 of the casing 20.

It is generally known in the art that in an electrostatic dust precipitator having a straight air flow passageway. the dust collecting efficiency decreases if when the dust particles are moved through the length of the passageway in the time period which is shorter than the time in which the ionized particles can be moved to the dust collecting electrode by the electrostatic attraction. If air to be cleaned were passed through the passageway at such a high velocity, no dust particles of any size could be satisfactorily trapped by the dust collecting electrode in a conventional air purifier using the electrostatic dust collection principle alone. Since, however, in the air purifier according to the present invention, air to be cleaned is passed therethrough in a spiral path, dust particles contained in the air stream are subjected to centrifugal force as the air circulates through the passageway 46, so that those particles which could not be collectedby dust collecting electrode 36 by the electrostatic attraction alone can be moved to the electrode 36 under the influence of centrifugal force even though air passes at a highvelocity through the spiral passageway 46. It is, moreover, said that dust particles than microns can be satisfactorily collected by thedust collecting electrode 36 even though the air is passed at a considerably high velocity through the air purifier, because the larger the particles are the greater the centrifugal forces imparted to the particles. An air purifier according to the present invention thus has outstanding features which include:

a. High dust collecting efficiency achieved essentially irrespective of the velocity and rate of flow of air passing through the air purifier and of the sizes of the dust particles contained in the stream of air. I

b. The dust collected is securely trapped by the dust collecting material.

0. Minimum efforts are required for maintenance and servicing of the air purifier and for exchange of parts.

d. Compact overall configuration resulting from the spirally configured air passageway.

It has been'assumed in the description of the embodiment shown in FIGS. 1 and 2 that the electrically conductive layers 38 and 38' are electrically connected to the porous of meshed electrically conductive layers 42, 42' and 42" as through the conductive plate 44, but they may be electrically isolated where desired. In this instance, the layers 42, 42' and 42" should be formed of an electrically non-conductive material and at the same time the plate 44 should be removed from the arrangement illustrated in FIG. 2.

Where desired, moreover, a deodorizing filter 69 may be located between the passageway 46 and the air outlet opening 32 for removing unpleasant odors from air to be discharged from the air outlet duct 34. A more detailed configuration of such a deodorizing arrangement is illustrated in FIGS. 4 and 5 which show a second preferred embodiment of the air purifier according to the present invention.

Referring to FIGS. 4 and 5, the deodorizing filter 69 is configured as generally cylindrical and has an open upper end which is in alignment with the air outlet openings 32 in the upper end wall 24 of the casing 20. The use of a deodorizing filter in an air purifier is in itself well known in the art and it has been an ordinary practice to have the filter fixedly held in place on, for example, the casing of the air purifier. Where the deodorizing filter is thus fixedly mounted on casing, badsmelling materials are accumulated on a limited area of the filter located in the path of air to be discharged from the air outlet opening 32, and the remaining area of the filter is kept intact. In the case of the air purifier configuration illustrated in FIGS. 4 and 5, air containing bad odors is passed locally through the area indicated as 69a of the filter 69 with the remaining area 69b kept intact throughout the use of the filter. This localized accumulation of materials will result in degraded deodorizing performance and a shortened life of the filter. Replacing the filter with a new one from time to time will require a disproportionate amount of time and labour and is therefore objectionable from an economical point of view.

For the purpose of eliminating this drawback, the lower end wall 26 of the casing 20 is formed with an opening 77 which is in alignment with the lower end of the deodorizing filter 69 and the opening 77 is closed by a closure 79 which is rotatably mounted on the lower surface of the lower endwall 26 of the casing 20 by means of fittings 81. The deodorizing filter 69 is securely connected at its lower end to the upper surface of this closure 79 and is thus rotatable about its axis within the casing 20 together with the closure 79. The angular position of the filter 69 relative to the path of air to be dischargedfrom the air outlet opening 32 is thus variable by turning the closure 79 on the lower end wall 26'of the casing 20 so that smell-containing materials can be accumulated substantially uniformly throughout the area of the filter 69 by turning the filter 69 about its axis from time to time. To facilitate turning of the closure 79, a knob 79a may be formed or mounted centrally on the lower surface of the closure 79, as shown.

In FIGS. 4 and 5, the air purifier embodying the present invention is shown as incorporating only one charging electrode 50 extending substantially centrally through the passageway 46 from the air inlet opening 28 to the air outlet opening 32, although more than one electrode 50 may be'employed if desired.

As previously mentioned, the lower end wall 26 of the casing 20 is arranged so as to be detachable together with the dust collecting electrode 36 to facilitate removal of dust particles deposited on the layers 42, 42 and 42" of the dust collecting material 36. If, in this instance, the lower end wall 26 of the casing 20 and the dust collecting electrode 36 supported by the end wall 26 are removed from the casing 20 with the charging electrode 50 inadvertently left energized by the hightension power source (not shown), a serious danger will be incurred on the operator. FIG. 6 illustrates an embodiment of an air purifier according to the present invention which eliminates such a danger.

Referring to FIG. 6, the cylindrical wall 22 of the casing 20 has formed at its circumferential edge portion adjacent the lower end wall 26 a pair of projections 76 and 76' extending radially outward from the cylindrical wall 22 and joined together at their ends by a wall portion 78. Spaced contact elements 80 and 80 are mounted on the inner faces of these projections 76 and 76, respectively in a manner to face each other at a certain spacing therebetween. The contact elements 80 and 80' are electrically connected to leads 82 and 82', respectively. As seen in FIG. 7, the lead 82 is connected to the source 84 of the dc.. high-tension voltage through an air purifier actuator switch 86 and a fuse 88.

The other lead 82' is connected through a booster transformer 90 to the charging electrode 50 of the air purifier.

On the other hand, the lower end wall 26 of the casing is formed with a radial projection 92 which is so located as to be in alignment with the projections 76 and 76' of the cylindrical wall 22 when the lower end wall 26 is attached in its working'position to the cylindrical wall 22. The projection 92 carries on its upper face an electric connector element 94 which is connectably received between the spaced contact elements 80 and 80 when the lower end wall 26 is assembled to the cylindrical wall 22 for thereby completing an electric path between the high-tension power source 84 and the charging electrode 50.

Through provision of the switching arrangement above described, the charging electrode 50 can be reliably disconnected from the high-tension power source 84 even though the air purifier actuating switch 86 is inadvertently left closed when the lower end wall 26 is removed together with the dust collecting electrode 36 for the purpose of purging the collecting electrode 36.

It is empirically known that the negative ions in atmospheric air act to tranquilize human nerves while positive ions act to the contrary. FIGS. 8 and 9 illustrate a fourth preferred embodiment of the air purifier according to the present invention arranged to utilize such a phenomenon. I

Referring to FIGS. 8 and 9, the air purifier includes in addition to the parts and elements incorporated in the embodiment shown in FIGS. 4 and 5, an ionizing electrode 96 which is located in the air outlet opening 32 in the upper end wall 24 of the casing 20. The ionizing electrode 96 is shown as being in a needle form and is supported by an outer casing 99 through a support 100 of an electrically conductive material. The support 100 is connected to a source (not shown) ofa negative high-tension dc. voltage for impressing a negative high-tension potential on the ionizing electrode 96 so that air being discharged through the air outlet opening 32 is ionized to a negative polarity. The embodiment above described is thus adapted not only to clean and deodorize the air but to ionize the air to the negative polarity such that it will soothe the human nerves. Where the air purifier having such features is installed in a motor vehicle, the same will contribute to safe driving while supplying satisfactorily cleaned air.

What is claimed is:

1. An air purifier comprising a generally cylindrical casing having an air inlet opening and an air outlet opening located substantially centrally of the casing, dust collecting wall means positioned within said casing and providing a continuous passageway extending spirally between the air inlet and outlet openings in said casing, said wall means including at least one dust collecting electrode for connection to a first electric terminal, and at least one charging electrode extending spirally in and along said passageway and electrically isolated from said collecting electrode, said charging electrode being for connection to a second electric terminal having a polarity opposite to the polarity of the first electric terminal for thereby establishing an electric field between the charging and collecting electrodes'so that particles of dust entrained in air directed into said passageway through said air inlet opening become ionized and are attracted to said dust collecting wall means as the air is circulated through said passageway from said air'inlet opening to said air outlet opening, said dust collecting wall means further including a dust collecting filter attached to the surface of said dust collecting electrode facing said passageway and an additional dust collecting electrode of a wire mesh form, said additional dust collecting electrode being attached to the surface of said dust collecting filter facing said passageway and electrically connected to the first named dust collecting electrode.

2. An air purifier as claimed in claim 1, further comprising deodorizing means located in said passageway immediately anterior to said air outlet opening, in which said deodorizing means in movable in situ relative to said air outlet opening so that the area passing the cleaned air through said deodorizing means is variable through changing the position of the deodorizing means relative to said air outlet opening.

3. An air purifier as claimed in claim 2, further comprising an ionizing electrode located in the neighbourhood of said air outlet opening and operative to be impressed with a negative high-tension power and a grounding electrode spaced from said ionizing electrode for ionizing to negative polarity the air being discharged from said casing through said air outlet open- 4. An air purifier as claimed in claim 3, in which said casing comprises an end wall supporting thereon said dust collecting wall means and releasable from said casing, and further comprising switch means mounted in part on said end wall and in part on a remaining portion of said casing for providing a releasable electrical connection between said dust collecting electrode and an electric power source, said electrical connection being interrupted when said end wall is released from said casing.

5. An air purifier as claimed in claim 3, further comprising an additional charging electrode located in said passageway immediately posterior to said air inlet opening for connection to a third electric terminal having a polarity which is similar to the polarity of said second electric terminal for thereby preliminarily charging the dust entrained in the air admitted to said passageway through said air inlet opening.

6. An air purifier comprising a generally cylindrical casing having an air inlet opening and an air outlet opening located substantially centrally of the casing, dust collecting wall means positioned within said casing and providing a continuous passageway extending spirally between the air inlet and outlet openings in said casing, said wall means including at least one dust collecting electrode for connection to a first electric terminal, and at least one charging electrode extending spirally in and along said passageway and electrically isolated from said collecting electrode, said charging electrode being for connection to a second electric terminal having a polarity opposite to the polarity of the first electric terminal for thereby establishing an electric field between the charging and collecting electrodes so that particles of dust entrained in air directed into said passageway through said air inlet opening become ionized and are attracted to said dust collecting wall means as the air is circulated through said passageway from said air inlet opening to said air outlet opening, and further comprising deodorizing means located in said passageway immediately anterior to said air outlet opening, in which said deodorizing means is movable in situ relative to said air outlet opening so that the area passing the cleaned air through said deodorizing means is variable through changing the position of the deodorizing means relative to said air outlet opening.

trode being for connection to a second electric terminal having a polarity opposite to the polarity of the first electric terminal thereby establishing an electric field between the charging and collecting electrodes so that particles of dust entrained in air directed into said passageway through said air inlet opening become ionized and are attracted to said dust collecting wall means as the air is circulated through said passageway from said air inlet opening to said air outlet opening, and an ionizing electrode located in the neighbourhood of said air outlet opening and operative to be impressed with a negative high-tension power and a grounding electrode spaced from said ionizing electrode for ionizing to negative polarity the air being discharged from said casing through said air outlet opening. 

1. An air purifier comprising a generally cylindrical casing having an air inlet opening and an air outlet opening located substantially centrally of the casing, dust collecting wall means positioned within said casing and providing a continuous passageway extending spirally between the air inlet and outlet openings in said casing, said wall means including at least one dust collecting electrode for connection to a first electric terminal, and at least one charging electrode extending spirally in and along said passageway and electrically isolated from said collecting electrode, said charging electrode being for connection to a second electric terminal having a polarity opposite to the polarity of the first electric terminal for thereby establishing an electric field between the charging and collecting electrodes so that particles of dust entrained in air directed into said passageway through said air inlet opening become ionized and are attracted to said dust collecting wall means as the air is circulated through said passageway from said air inlet opening to said air outlet opening, said dust collecting wall means further including a dust collecting filter attached to the surface of said dust collecting electrode facing said passageway and an additional dust collecting electrode of a wire mesh form, said additional dust collecting electrode being attached to the surface of said dust collecting filter facing said passageway and electrically connected to the first named dust collecting electrode.
 2. An air purifier as claimed in claim 1, further comprising deodorizing means located in said passageway immediately anterior to said air outlet opening, in which said deodorizing means in movable in situ relative to said air outlet opening so that the area passing the cleaned air through said deodorizing means is variable through changing the position of the deodorizing means relative to said air outlet opening.
 3. An air purifier as claimed in claim 2, further comprising an ionizing electrode located in the neighbouRhood of said air outlet opening and operative to be impressed with a negative high-tension power and a grounding electrode spaced from said ionizing electrode for ionizing to negative polarity the air being discharged from said casing through said air outlet opening.
 4. An air purifier as claimed in claim 3, in which said casing comprises an end wall supporting thereon said dust collecting wall means and releasable from said casing, and further comprising switch means mounted in part on said end wall and in part on a remaining portion of said casing for providing a releasable electrical connection between said dust collecting electrode and an electric power source, said electrical connection being interrupted when said end wall is released from said casing.
 5. An air purifier as claimed in claim 3, further comprising an additional charging electrode located in said passageway immediately posterior to said air inlet opening for connection to a third electric terminal having a polarity which is similar to the polarity of said second electric terminal for thereby preliminarily charging the dust entrained in the air admitted to said passageway through said air inlet opening.
 6. An air purifier comprising a generally cylindrical casing having an air inlet opening and an air outlet opening located substantially centrally of the casing, dust collecting wall means positioned within said casing and providing a continuous passageway extending spirally between the air inlet and outlet openings in said casing, said wall means including at least one dust collecting electrode for connection to a first electric terminal, and at least one charging electrode extending spirally in and along said passageway and electrically isolated from said collecting electrode, said charging electrode being for connection to a second electric terminal having a polarity opposite to the polarity of the first electric terminal for thereby establishing an electric field between the charging and collecting electrodes so that particles of dust entrained in air directed into said passageway through said air inlet opening become ionized and are attracted to said dust collecting wall means as the air is circulated through said passageway from said air inlet opening to said air outlet opening, and further comprising deodorizing means located in said passageway immediately anterior to said air outlet opening, in which said deodorizing means is movable in situ relative to said air outlet opening so that the area passing the cleaned air through said deodorizing means is variable through changing the position of the deodorizing means relative to said air outlet opening.
 7. An air purifier comprising a generally cylindrical casing having an air inlet opening and an air outlet opening located substantially centrally of the casing, dust collecting wall means positioned within said casing and providing a continuous passageway extending spirally between the air inlet and outlet openings in said casing, said wall means including at least one dust collecting electrode for connection to a first electric terminal, at least one charging electrode extending spirally in and along said passageway and electrically isolated from said collecting electrode, said charging electrode being for connection to a second electric terminal having a polarity opposite to the polarity of the first electric terminal thereby establishing an electric field between the charging and collecting electrodes so that particles of dust entrained in air directed into said passageway through said air inlet opening become ionized and are attracted to said dust collecting wall means as the air is circulated through said passageway from said air inlet opening to said air outlet opening, and an ionizing electrode located in the neighbourhood of said air outlet opening and operative to be impressed with a negative high-tension power and a grounding electrode spaced from said ionizing electrode for ionizing to negative polarity the air being discharged from said casing through said air outlet opening. 